This invention relates to fasteners and more particularly to an improved method of an apparatus for setting blind fasteners and to improved fasteners adaptable for use with the improved method and apparatus.
Blind fasteners are utilized to fasten two pieces of material together when only one side of the work is accessible to the fastening tool.
While many different tools and methods of setting blind fasteners have been devised, the clamp-up provided to the set fastener thereby has not, in many cases, been as firm as some applications may demand. In addition, in many cases, previous methods and apparatus have provided sets where the pieces of material being fastened are not held flush against each other.
The reasons for these failures in the prior art fasteners is principally because only one side of the fastener was effectively worked by the fastening apparatus.
For example, a typical blind fastener comprises a hollow barrel portion and a flat annular flange at one end thereof. A mandrel that is similar to a headed nail is mounted in the barrel portion of each fastener with the shank of the mandrel extending out of the flange end of the fastener. The head of the mandrel protrudes out the barrel portion of the fastener. The fastener is set by pulling the mandrel shank with an appropriate tool, such as that shown in U.S. Pat. No. 3,164,283, so that the head of the mandrel deforms the far side of the fastener and thus captures the pieces of material to be set between the deformed far side of the fastener barrel portion and the fastener flange.
However, with this arrangement, the setting action of the mandrel is limited by the strength of the barrel portion material and the pulling force exerted by the fastener tool. In many instances, the pulling force is not strong enough to force the upset material back into the rear of the work so as to tightly clamp the material between the upset part of the barrel portion and the fastener flange.
Another problem encountered with this arrangement is that if the pieces of material to be set were not held together prior to the setting operation, the initial upsetting of the far end of the fastener would "freeze" the front piece of material on the fastener barrel portion adjacent the upset. At this point, there was no way to bring the pieces of material together on the fastener. Thus, the rear pieces of material were movable laterally on the fastener between the frozen piece and the flange. This was obviously undesirable.
Attempts to improve the set of a fastener by performing operations on both sides thereof, such as that disclosed in U.S. Pat. No. 2,477,056, were not satisfactory in that the rear setting operation was weak and no operation was performed to bring the pieces of material to be set together before the final setting operation was completed.
The inventor of the method, apparatus and fasteners described herein has previously devised the improved fastening apparatus disclosed in U.S. Pat. No. 3,763,541, which provided a substantially stronger set than those provided theretofore and, in addition, removed the necessity of providing a mandrel with each fastener, a significant cost saving. However, even with the substantially stronger setting force, there were instances when the pieces of material being set were not clamped together and set in that position, particularly when the first piece of material was "frozen" by the initial setting action.